Numerous patents have issued disclosing organic compounds as stabilizers for 1,1,1-trichloroethane. One of the earliest patents granted, U.S. Pat. No. 2,838,811, disclosed that 1,4-dioxane (the cyclic diether derived from diethylene glycol) alone or in combination with a nonprimary acetylenic alcohol was useful to stabilize 1,1,1-trichloroethane. Previously, secondary and tertiary butyl alcohols have been added as storage stabilizers. These butanol-stabilized compositions have limited effectiveness in cold cleaning of aluminum and its alloys but seem suitable for iron, and its alloys. With the increased demand for this unique solvent because of its relative safety, i.e., no Tag Open Cup flash point and high threshold limit value (TLV), into, for example, hot cleaning, i.e., dipping metal parts into warm or hot (boiling) 1,1,1-trichloroethane, research efforts to find a suitable stabilizer for 1,1,1-trichloroethane-white metal reaction resulted in the discovery of 1,4-dioxane. Since this first patent, directed specifically to solving 1,1,1-trichloroethane's unique problem of reactivity toward white metals (aluminum and zinc), some 90 to 100 patents have issued to inventors in the United States alone. These patents disclose literally hundreds of organic compounds as suitable for stabilizing 1,1,1-trichloroethane in the presence of metals, particularly aluminum. However, of these hundreds of compounds only a few, less than 10 in number, have found commercial acceptability in the marketplace principally because outside of these 10, the remainder require impractically high concentrations, or are expensive, or are in short supply, and/or perform unacceptably under the general use conditions found in industry. A few, again less than 10, have found limited commercial acceptability in special areas such as aerosols, film cleaning and the like, where careful control by the user is taken to avoid contact with aluminum.
Since the introduction into the marketplace in 1957-1958 as a commodity the largest volume of 1,1,1-trichloroethane sold throughout the world contained, and still contains, 1,4-dioxane, nitromethane and 1,2-butylene oxide as the sole inhibitors. The next largest volume has been that containing 1,3-dioxolane (a five-membered dioxygen heterocycle, a compound very similar to 1,4-dioxane), nitromethane, 1,2-butylene oxide and in most instances one or more materials (such as lower ketones and/or alcohols which accounts for the remainder of the ten principal compounds used in industry to stabilize 1,1,1-trichloroethane).
Aerosol and film cleaning uses do not require stabilization to the same type as metal cleaning applications which latter subject the 1,1,1-trichloroethane to the most severe physical and chemical stresses. Therefore, in aerosol applications, not only is less stabilizer present but less effective stabilizers can be employed. Most stabilizers for 1,1,1-trichloroethane aerosol usage are ones which do not create odor problems when mixed with the components of aerosol formulations. Film cleaning 1,1,1-trichloroethane compositions contain stabilizers which do not dissolve the emulsions from photographic film. Many of the 1,1,1-trichloroethane solvents sold into the aerosol market contain methylal (dimethoxymethane), am alkylene oxide, e.g., propylene oxide, and an alcohol, e.g., secondary or tertiary butyl alcohol.
In the light of recent attacks by environmentalists on some of the chlorinated hydrocarbons allegedly due to their environmental hazards as well as controls concerning their use resulting from the recently enacted Occupational Safety and Health Act, it becomes necessary for the manufacturers of 1,1,1-trichloroethane to provide this safer solvent, from an environmental, safety and health standpoint, with inhibitor systems which will be in conference with environmental standards.
It is the object of the present invention to provide an industrially useful combination of stabilizers for 1,1,1-trichloroethane which will inhibit, even under the severe stress of vapor degreasing, the 1,1,1-trichloroethane-aluminum reaction as well as the reactions attributable to the presence of zinc, copper and iron, their alloys, and water.
These and other objects will become apparent to those skilled in the art from the following description and claims.